Light guides, and more specifically optical fibers, can conveniently be used for remote sensing. Currently, there are a number of applications where optical fibers are used for single point or distributed sensing, in order to monitor temperature and/or pressure in a given environment, using for instance Fiber Bragg Grating (FBG) technology.
In particular, in the medical field, optical fibers are also used since years, at least at an investigational level, for in-vivo radiation monitoring, in different fields, such as radiation therapy and nuclear medicine. In these domains, the fibers are used, possibly in combination with a radiation detector, in order to guide the light generated by the exposure to ionizing radiation, to an external reader.
As a specific example of medical dose monitoring, the fields of interventional procedures and of brachytherapy are discussed hereinafter.
Interventional procedures in cardiology are widely used, as a minimally invasive alternative to surgical interventions. The entire procedure is based on the (intensive) use of fluoroscopic imaging in order to follow the patient's anatomy in real-time and to visualize the position of catheters and other tools during insertion. However, imaging with X-rays does also imply exposure of patients (and staff) to ionizing radiation. Particularly in complex procedures, the doses absorbed by different organs can be quite high.
In a recent study performed by E. Vano (Implications for medical imaging of the new ICRP thresholds for tissue reactions, presented at the International Commission on Radiological Protection symposium, 22 Oct. 2013, Abu Dhabi), where 4128 patients were included, it is shown that in a period included between 2010 and 2011, 16% to 27% of the patients undergoing a cardiac interventional procedure at the San Carlos university hospital in Madrid, were exposed to a cardiac radiation dose of at least 500 mGy and to a lung dose of at least 1000 mGy. As a comparison, 0.1 mGy is the dose associated with an X-ray lung radiography and 2000 mGy is the typical dose imparted to a tumour daily, in radiation therapy.
In recent studies it has been shown that exposure of the heart to ionizing radiation, severely increases the risk of heart failure and that there are a number of cardiac pathologies that are strictly linked to radiation exposure (S. W. Yusuf et al., Radiation-Induced Heart Disease: A Clinical Update, Cardiology Research and Practice, 2011). Because of the societal impact of this problem, these results were also commented by the Economist in an article of Jul. 13, 2013 entitled How can radiation therapy cause heart disease?
Shortly, systematic dose monitoring will give the following advantages:                Provide an accurate measurement of the radiation dose delivered to the patient during cardiology interventional procedures.        Empowerment of patients by giving them real, measured radiation doses, instead of estimations. Therefore potential risks can be correctly understood and anticipated.        Quality label for cath labs: lower dose for the same interventions will be associated with higher healthcare quality standards.        Operator awareness: a dose measurement device will be an additional tool for cardiologists to monitor their performances.        
On the therapy side, High Dose Rate, HDR, brachytherapy is used as an effective treatment in a select group of breast cancer patients. Whereas in “classical” radiation therapy, patients are irradiated over 6 to 7 weeks, 5 days a week, in HDR brachytherapy, a higher dose is typically imparted per fraction (5 Gy instead of 2 Gy) so that a total of 10 fractions over 5 days (patients are irradiated twice a day) completes the entire treatment.
In breast HDR brachytherapy, the dose is delivered through the insertion in the tumour of a number of radioactive Ir-192 sources. The kinematic of these sources (i.e. their position as a function of time), along with their activity, define completely the final dose distribution in the tumour and in the surrounding healthy breast tissue.
The expected dose is calculated by a software (treatment planning system) that makes a number of approximations on the actual patient anatomy.
Nowadays there is no commercially available system allowing an in-vivo, real-time dose measurement at several points, in a convenient, user-friendly and possibly economical way, so that it can be easily and systematically integrated within a clinical workflow. It would be an advantage to have a system available that would allow measuring the imparted dose, at different locations, in a minimally invasive way.
In WO2012159201A1, systems and methods are described to perform dosimetric measurements using a plurality of scintillating elements, on one optical fiber. These elements may be contiguous or located at a certain distance from each other. Different kind of scintillating materials can be used. Alternatively, the same material can be used for all elements. In this case band-pass filters have to be glued, between each pair of scintillating elements.
The response of the different scintillators is obtained by deconvolving the total spectrum, using signal processing tools. The actual number of scintillators admitted on the fiber is limited by the fact that their spectra have to differ, at least in part, in order to be able to separate the contribution coming from each of them. In other words, the actual spatial resolution that they can achieve, is limited by the dimensions of the scintillators used and by their number (the latter being limited by the fact that the spectra of the different scintillators should differ and by the overall mechanical robustness of the system). When using the same material for all scintillating elements on the fiber, spatial resolution can be lost by the fact that a band-pass filter is needed in between the different scintillators. Furthermore, the overall mechanical stability of the fiber may be compromised when gluing (contiguously or non-contiguously) many scintillators and/or filters on it.
In U.S. Pat. No. 6,782,289, system and methods are presented to perform dose measurement in a body's blood vessels, after having injected a radioactive marker. This marker will eventually accumulate on plaques in the arteries and their radioactivity is measured by the system presented. More specifically the system disclosed in U.S. Pat. No. 6,782,289 can only measure scintillation coming from one region (the plaque loaded with radioactive tracer). In this case, a single detector is fixed at one position on the fiber.
In US20020087079A1 a system is described wherein a scintillator is integrated in a catheter, and optical guides are used to bring the light produced from the scintillator to the reader. This system is only capable of measuring a dose at one location, in correspondence with the scintillating element.
In U.S. Pat. No. 5,811,814A, yet another system is illustrated, wherein a single scintillating element, along with an optical fiber, are incorporated in an intravascular catheter. Also this system, as some of the ones previously discussed, is able to measure a dose only at one location.
In US20060153341A1 and US20090236510A1 systems are presented, allowing multi-point radiation detection. However, according to both descriptions, the use of a plurality of light guides is needed to collect the light produced at the different points.